Vibration damping materials are used to prevent vibration and noise of various structures to insure sustained quietude. The vibration damping materials have been widely used beneath cabin floors of automobiles or applied to rolling stock, ships, aircraft, electric machines, buildings, construction machines, and the like. Molded products such as plate products and sheet products produced using materials having vibration absorbing performance and sound absorbing performance have been conventionally used as raw materials used for such vibration damping materials. However, it is difficult for such molded products to be used at vibration- or noise-generation positions having complicated shapes. Therefore, various methods for improving the workability and thereby sufficiently exhibiting the vibration damping property have been investigated. That is, an inorganic powder-containing asphalt sheet has been installed beneath cabin floors of automobiles, for instance, but since the sheet must be secured in position by thermal fusion, improvements in workability and the like are needed. Therefore, studies on various compositions or polymers for vibration damping for forming the vibration damping materials have been made.
Coating vibration damping materials (coating materials) have been developed as an alternative material for such molded products. For example, the following vibration damping coating material has been variously proposed: a vibration damping coating material is sprayed onto positions to be subjected to damping treatment with a spray or applied thereto by any method, and the thus-formed coating film can give a vibration absorbing effect and a sound absorbing effect. Specifically, an aqueous vibration damping coating material prepared by the following manners: mixing synthetic resin powders with a vehicle such as asphalt, rubber, and synthetic resin; and improving the hardness of the obtained coating film, has been developed. In addition, as materials suitably used for interior parts of cars, vibration damping coating materials prepared by dispersing activated carbon as a filler into a resin emulsion has been developed. Such vibration damping coating materials and the like need to be excellent in vibration damping property and mechanical stability. However, these conventional items are still insufficient in vibration damping performances. Therefore, a technology which enables vibration damping materials to exhibit more sufficient vibration damping performances in addition to excellent mechanical stability has been desired. If the vibration damping coating material is formed on an object, the coating material is dried by heating at a high temperature, for example, by baking, in an industrially used drying line. If a conventional emulsion for vibration damping materials is coated on a vertical or inclined surface, the coating material on the coating surface sags during or after the heating in some cases. Therefore, an emulsion for vibration damping materials, which shows the following excellent resistance to coating film collapsibility has been needed: the coating film does not collapse, for example, it does not sag, even when it is dried by heating in an industrially used drying line; and an excellent coating film can be formed on the vertical or inclined surface. Further, such a vibration damping coating material is stored and used in cold regions. Therefore, a vibration damping coating material which is excellent in low-temperature storage stability in order to maintain its usable state without freezing and the like under low temperatures also has been desired.
With respect to a conventional raw material for vibration damping materials, Japanese Kokai Publication No. 2004-137485 on pages 1 and 2 discloses a thickener for aqueous vibration damping materials, including a polymer containing an alkali-soluble monomer unit and an associative monomer unit. A coating material containing this thickener for aqueous vibration damping materials is excellent in drying property and can sufficiently prevent cracks or blisters generated on the surface, and thereby high-quality vibration damping materials excellent in vibration damping property can be provided. Therefore, such a coating material has been industrially useful. However, such a thickener for aqueous vibration damping materials has room for improvement in order to be more preferably used as a raw material for vibration damping materials of various structures by further improving the physical properties such as vibration damping property, drying property, and mechanical stability.
Further, Japanese Kokai Publication No. 2006-257395 on pages 1, 2, 12, and 13 discloses an emulsion composition containing a synthetic resin and an nonionic compound which is prepared by adding an ethylene oxide and an alkylene oxide containing 3 or more carbon atoms randomly and/or in block to an aliphatic alcohol containing 18 carbon atoms or less and which has a specific molecular weight. Japanese Kokai Publication No. 2006-257395 discloses that this composition does not sag under drying at a high temperature, but the coating film having a thickness of as small as 25 μm is subjected to the liquid dripping test. Therefore, there is room for improvement in order to form a composition capable of forming a coating film which does not sag even if the film has a large thickness.
Further, Japanese Kokai Publication No. 2005-105106 on pages 1 and 2 discloses an emulsion for vibration damping materials, including a polymer and an emulsifier. Such an emulsion contains 3% by weight or less of a nonionic emulsifier as the emulsifier relative to the total amount of the monomers used for forming the polymer. This composition can form a coating film which neither sags nor drops, but such a composition still has room for improvement in order to more effectively exhibit these effects.
As a conventional composition for vibration damping materials, which forms a vibration damping material, the following emulsion-containing copolymer latexes are disclosed. Japanese Kokai Publication No. Hei-09-104842 on pages 1 and 2 discloses an aqueous damping coating composition including at least one vehicle selected from a synthetic resin emulsion and an asphalt emulsion. Japanese Kokai Publication No. Hei-11-29737 on pages 1 and 2 discloses a copolymer latex for aqueous coating, obtained by copolymerizing an aliphatic conjugated diene monomer, an ethylene unsaturated carboxylic acid monomer, and the like, in the presence of an α-methylstyrene dimer. Japanese Kokai Publication No. 2000-178497 on pages 1 and 2 discloses a copolymer latex for chipping-resistant coating material, obtained by subjecting a conjugated diene monomer, an ethylene unsaturated carboxylic acid amide monomer, an ethylene unsaturated carboxylic acid monomer, and the like to emulsion polymerization in the presence of an inorganic persulfate polymerization initiator. Japanese Kokai Publication No. 2000-178498 on pages 1 and 2 discloses a copolymer latex for vibration damping material, obtained by subjecting a conjugated diene monomer, an epoxy group-containing ethylene unsaturated monomer, an ethylene unsaturated carboxylic acid alkyl ester monomer, and the like, to emulsion polymerization. Japanese Kokai Publication No. 2000-178499 on pages 1 and 2 discloses a copolymer latex for vibration damping material, obtained by subjecting a conjugated diene monomer, an epoxy group-containing ethylene unsaturated monomer, an ethylene unsaturated carboxylic acid amide monomer, and the like to emulsion polymerization.
However, these technologies fail to provide a vibration damping material which can attain both excellent thermal drying property and excellent vibration damping property. That is, in the case where the synthetic resin emulsion or the asphalt emulsion is used, blisters tend to be generated on the coating film surface when the coating film is formed by thermal drying because moisture in an undried coating film tries to evaporate. Therefore, there is room for improvement in the thermal drying property. Further, if a copolymer latex composed of a conjugated diene monomer and other monomers is used, the monomer unit derived from the conjugated diene monomer does not exhibit sufficient vibration damping property. Therefore, such a copolymer latex still has room for improvement in order to satisfy excellent thermal drying property and vibration damping property.
With regard to an aqueous dispersion containing acrylic polymer particles that are composite particles each composed of a core part and a shell part, Japanese Patent No. 2904995 on pages 1 to 3 discloses that such an aqueous dispersion can be prepared using a reactive anionic surfactant and that the thus-obtained aqueous dispersion is preferably used to form a chipping material. Such an aqueous dispersant is preferably used to form a chipping material and it can form a hard coating film which is hardly scarred. Such a coating film property is emphasized and therefore, in order to be spray-coated, such an aqueous dispersant is determined to have a low viscosity. However, with regard to vibration damping materials, it is preferable that the vibration damping materials form a hard coating film, but softness of the coating film is also important. Further, the composition for vibration damping materials is prepared to have a relatively high viscosity in order to form a thick coating film. Accordingly, such a composition has room for improvement in order to be preferably used as a vibration damping composition having such characteristics, and further in order to be excellent in vibration damping property or thermal drying property and hardly changed with time.
Japanese Kokai Publication No. 2004-277603 on pages 1 and 2 discloses an emulsion for vibration damping materials, including an emulsion obtainable by emulsion polymerization of a monomer component using a reactive emulsifier. This emulsion for vibration damping materials is excellent in characteristics such as vibration damping property and thermal drying property. However, such an emulsion still has room for improvement in order to be directly coated not only on a horizontal surface but also on an inclined surface and then dried, thereby forming a coating film which exhibits high vibration damping property.
As the resin emulsion used in the vibration damping material application, an acrylic emulsion having a core-shell structure and the like has been used. However, the acrylic emulsion delays a polymerization reaction when a polymer is produced, and due to this, mixing of the monomer constituent of core part and that of shell part is caused, resulting in insufficient localization. The polymer in which the localization of the monomer components is insufficient does not exhibit high vibration damping property. Therefore, in order to obtain a polymer which exhibits high vibration damping property by preventing such delay of the polymerization reaction, a method of introducing (meth)acrylic acid ester such as methyl methacrylate into a polymer has been used. However, according to this method, production costs are increased. Therefore, a method for more inexpensively producing an acrylic emulsion in which the mixing of the monomer constituent of core part and that of shell part is not generated has been needed.
With regard to a conventional emulsion for vibration damping materials, Japanese Kokai Publication No. 2005-281577 on pages 1 and 2 discloses a copolymer emulsion for vibration damping materials, prepared by copolymerizing a monomer mixture essentially containing an acrylic monomer. However, this copolymer emulsion for vibration damping materials is produced from a monomer mixture containing 25% by weight or more of methyl methacrylate. Therefore, there is still room for improvement in that a copolymer emulsion which exhibits high vibration damping property or mechanical stability and also exhibits excellent low-temperature storage stability and in which mixing of the monomer constituent of core part and that of shell part is not generated is produced more inexpensively.
Japanese Kokai Publication No. 2005-187514 on pages 1 and 2 discloses a vibration-damping water-based coating composition including: an urea compound; a filler; and a foaming agent; and a synthetic resin emulsion essentially including an α,β-unsaturated carboxylic acid and at least one monomer selected from α,β-unsaturated carboxylic acid ester monomers, aromatic vinyl monomers, and diene monomers, in which the glass transition temperature (Tg), the maximum value of the loss angle tangent, and the average particle diameter are specified. Further, Japanese Kokai Publication No. Hei-10-324822 on pages 1 and 2 discloses a vibration-damping water-based coating composition essentially containing a filler and a resin emulsion in which the Tg, the loss angle tangent, and the average particle diameter of the resin particles are specified. However, these compositions also have room for improvement in order to exhibit more excellent vibration damping property or mechanical stability, and have excellent low-temperature storage stability.